1. Field of the Invention
The present invention relates to a method for evaluating a quality of a semiconductor substrate, and more particularly, to a method for evaluating metal contamination within the substrate. The present invention further relates to a method for manufacturing a semiconductor substrate, making it possible to provide high-quality semiconductor substrates by identifying a non-defective product using the above method for evaluating a quality of a semiconductor substrate.
2. Discussion of the Background
Inspection methods involving observing bright points on a surface of a semiconductor substrate that are detected by a foreign matter inspection device have been proposed as methods for evaluating the quality of silicon epitaxial wafers, mirror-finished wafers and the like. In these inspection methods, surface particles, crystal originated particles (COP), dislocations, and the like, as well as various surface pits due to the crystal quality of the substrate, are detected as bright points. Since particles on a substrate are observed as protrusions and surface pits are observed as indentations, the causes of bright points resulting from particles and surface pits can be identified to a certain degree.
In mirror-finished wafers, metal ions contained in the slurry used for mirror polishing diffuse into the wafer during the mirror polishing process, creating a problem by contaminating the bulk near the surface. Wafers that have been contaminated by metal in this fashion develop surface crystal defects and surface roughness, compromising quality. Thus, identification of the elements of the various metal impurities present in the bulk near the surface of a semiconductor substrate provides clues to discovery of causes thereof, and thus relates to improvement of the manufacturing process. However, since the crystal defects and surface roughness caused by metal contamination do not appear in the form of protrusions or indentations on the surface of the substrate, they are normally not detected as bright points during inspection by foreign matter inspection devices, and present a risk of a defective substrate being shipped as a non-defective product.
Accordingly, a method has been proposed for identifying metal contaminants in the bulk near the substrate surface by observing, with a foreign matter inspection device, the shape of bright points on the substrate surface following cleaning and comparing this shape to the shapes of bright points on a cleaned reference wafer into which known heavy metals have been diffused. Such a method is described, for example, in Japanese Unexamined Patent Publication (KOKAI) No. 2000-193597, which is expressly incorporated herein by reference in its entirety. However, this method involves a complex process requiring the observation of the shapes of various bright points and their comparison to the shapes of bright points on the reference wafer. There are thus problems in that evaluation is time-consuming and the method lacks practicality.